If you get there, you will speak fluently and rarely make grammatical mistakes that bother native speakers. You may still have to search for a word occasionally, but will be able to come up with another way to say what you want. You will be able to talk about a full range of topics and deal with people on a professional level.

You can expect to spend months or even years in the language community before you reach this level, as it involves sociolinguistic competence. This proficiency can only be developed by experiencing language in a large number of social situations.